Voiv. 6, 1920 
PETROLOGY: G. P. MERRILL 
457 
IV. Secondary Borders about Chondniles. — A not uncommon feature 
of the chondrule is the narrow border or rind about the circumference. 
These borders as a rule, are of lighter color than the interior, of a clear, 
more pellucid nature, though it may be including portions of the minerals 
characteristic of the matrix in which they are embedded. This is well 
shown in the olivine chondrule, figure 12. This border has an appear- 
ance at once suggestive of the secondary intergrowth or enlargement often 
seen in feldspars and other minerals of terrestrial rocks. The later por- 
tions sometimes, though not always, have the same optical orientation 
as the interior. I am not certain if this border is of a like nature to that 
described by Tschermak about some of the chondrules of the Grosnaja 
stone and which he considered of secondary origin. In some instances 
FIG. 13 
the chondrules are surrounded by an irregular border of metal or metallic 
sulphide. 
V. Double or Compound Chondrules .—Occsisional forms are met with 
in which a large crystal of olivine or pyroxene is inclosed by a border of 
finer crystals of the same mineral but suggestive of a later generation. 
More common are forms such as are shown in figure 13. The crystals 
are of enstatite but the larger one is filled with minute cavities which are 
lacking in the smaller forms. Of greater interest is the occasional oc- 
currence of a chondrule within the mass of a second or larger form, as 
figured by Tschermak, on plate 8, figure 1, of his Besckafenheit. I will 
refer to this also, later. 
The descriptions thus far given are of the most perfectly formed and 
ou'tlined chondrules only. The broken, angular and, in some cases, dis- 
torted radiate enstatite forms are plainly mechanical derivatives, and while 
they have a bearing upon the origin of the masses in which they occur, 
